Thermionic valve



J. FOSTER THERMIONIC VALVE Feb. 22, 1949.

2 sheets-sheet 1 Filed Oct. 28. 1942 Invenior Jan, 'Faster'.

Attorney Feb. 22, 1949. J. FOSTER THERMIONIC VALVE I Filed om. 2a, 19422 Sheets-Sheet 2 MMV Attorney Patented Feb. 22, 1949 THERMIONIC VALVE.lohn Foster, London, England, assignor, by mesne assignments, toInternational Standard Electrie Corporation, New York, N. Y., acorporation of Delaware Application October 28, 1942, Serial No. 463,701In Great Britain December 19, 1941 8 Claims.

. The present invention relates to electron discharge devices for use atultra high frequencies of the kind in which the electron stream isdensity modulated by controlling the iiow of electrons from the cathodeand the density modulated beam is employed to excite a hollow resonatorfrom which the output is obtained.

Such devices of the type specified have many advantages over other knownelect-ron discharge devices for use at ultra high frequencies, such asthose working on the electron velocity modulation principle or electrondeflection principle. in particular the noise level in devices in whichthe electron ow is controlled is much lower than in the other types.

In order to adapt the well known grid controlled electron owmultielectrode valve comprisingA a cathode, anode and control grid foruse at ultra high frequencies, it is necessary to eliminate troubles duefirstly to electron transit time eiiects, and secondly to the couplingbetween the input and output circuits in the form of interelectrodecapacities, and selfand mutual-inductances of the leads.

The troubles due to the coupling between the input and output circuitshave been overcome in the kind of device to which this invention relatesby using the density modulated beam to excite a resonant chamber fromwhich the output is taken. Such a device operates eiciently as a wideirequency-band amplifier, and has a low noise characteristic as opposedto beam velocity and deflection controlled devices.

Itis the object of this invention to provide an improved device of thekind hereinbefore specied of simpler construction than known devices ofthat kind.

According to the invention such a device comprises a cathode, acontrol'grid and an anode or collecting electrode, a U-shaped metallicmember containing said cathode and control grid parallel to the basethereof, a pair of metallic plates spaced in the direction of electronflow from the limbs of said U-shaped member to form a first gap betweensaid plates and limbs and spaced from the anode or collecting electrodeto form a second gap between said plates and anode and a metallic discsealed into the Wall of the device and having an aperture therein toallow of the passage of the electron stream therethrough and adapted toform a part ofv a hollowl resonator' arranged to be inductively excitedby the passage of the electron stream across the said second gap.

The invention will be further described by way of example as embodied inthe electron discharge device illustrated in the accompanying drawings,in which Figures 1, 2 and 3 are plan, side and end views respectively,with the glass envelope of the device shown in section, as well as theouter wall of the resonator in Fig. l, Figure 14 shows a detail insection.

Referring to the drawings, the electron discharge device comprises anelectrode assembly which consists of a cathode l, control grid 2 andsecond grid 3. The cathode is connected to a u -shaped electrode 4 whosebase is constructed to form a Condenser, with a plate v2 as hereinafterdescribed in connection with Fig. Ll. The grid 3 is connected to thiscondenser by a very short lead l5 of low self inductance. 'This almostclimi. nates any tendency to instability. The leads 5 and 5a areconnected to the control grid 2 by means of a short conductor 29 and theleads c and Ea are connected to the cathode by means of conductor 22.These leads form a comparatively low loss path for the introduction ofthe signal. The input circuit between 5 and 6 or Ea and 6a couldconveniently be a screened Lecher system. The cathode heater currentleads 'i and 8 are passed through the press I6 in well-known manner aswell as the D. C. voltage lead 9 for grid 3.

One side only of the cathode l is coated with electron emissive materialand the electrons after passing through grid 3 are formed into a narrowbeam indicated at il by the electron lens formed by the gap IB betweenshields id and U-shaped electrode 4. This beam passes through anaperture I2 in a copper disc Il sealed in .the glass envelope andimpinges on the anode i3.

The electrodes 4 and l0 are mounted on rods or wire bars which aresupported in two parallel mica plates i9 and 20. Springs 2l are mountedon and in direct electrical contact with two of the said bars, and whenthe electrode assembly is placed in position the springs press againstthe disc I l and so make good electrical connection between the disc Hand the shield electrodes it.

The condenser incorporated in the base ci the U-shaped electrode i isshown more clearly in Figure 4 and compri-ses a metal plate 2isandwiched between two sheets of mica, as shown in the drawing. Thesethree elements are then sandwiched between the bottom of the U-shapedelectrode and a channel shaped member 2i' the ends of which are.soldered or welded to the limbs of the electrode 4. The centre plate 'ioi the condenser is provided with a tab at each end thereof. In Fig. 4,only one tab 26 is visible, the position of the other tab 25 being shownin the drawing. lOne of these tabs, namely 25 is connected to the grid 3by the short lead I5, as already stated and the other tab 24 isconnected to the lead 9 which is brought out through the press I6 andenables a positive potential to be applied to the grid 3. The otherplate of the condenser formed by the base of the electrode 4 and member2| is connected to the cathode by means of a connector 22.

The ends of the electrodes I are brought in close proximity to eachother and are provided with parallel portions 23 which pass through theaperture I2 in the disc Il and enable the input structure to be alignedwith the aperture I2. The length of these portions 23 may be such as toleave a gap between these members and the anode I3 of the order of .100inch. Y

In use a high-Q coaxial resonator 26 (Fig. 1) is plaoed on the anode I3and disc II or other resonant chamber may be mounted on the disc I I topresent a high impedance to the beam.

When an ultra-high-frequency -signal is fed into the grid 2 the beambecomes space-chargedensity Imodulated and thus excites inductively theoutput resonator as it passes from the aperture I2 to the anode I3. Asthis time is short the output efliciency is very nearly 100%. Thetransit time of the electrons from cathode to anode introduces a phasechange between the input and output voltages, but is otherwise of noimportance. The use of reasonably hiigh voltages enables the distancefrom the anode I3 to the aperture I2 to be quite large thus rieducingthe output capacity to a low value.

The voltages applied to the control grid may be of the order of -1.5.volts, to the grid 3 of the order of 150 volts, to the disc II, shieldelectrodo I0 and anode I3 of the order of 700" volts, and the U-shapedelectrode li at zero volts or cathode potential.

In one practical case Mif- Input capacity 6.0 Output capacity 0.5 YFeedback capacity .0005

The emission current was 8.0 ma., and was controlled by the potential onthe control grid giving a slope of the characteristic curve of 6.5ina/v.

Gain at 600 megacycles per second with 4 rnegacycles per second bandWidth=28 decibels.

The advantage of the electron discharge device according to theinvention for amplification of ultra high frequencies are:

(l) Elimination of input damping due to cathode lead inductance.

. (2) Elimination of instability, the accelerating grid 3 to cathodedecoupling condenser (contained within the base of the U-shapedelectrode il) being connected to these electrodes by short leads of lowindu-ctance.

(3) Low output capacity enabling use of a high Q resonator, therebyincrea-sing the gain and increasing the frequency band width.

(4) Elimination of instability due to anodegrid capacity, this beingreduced to a negligible quantity.

(5) The low noise characteristic of spacecharge controlled devices asopposed to Velocity and deiiection controlled devices.

What is claimed is:

1. An electron discharge device for use at ultra high frequenciescomprising a cathode, a control grid, and an anode, a U-shaped metallicmember having flat parallel limbs containing said cathode and gridspaced from the base thereof, a pair of metallic plates substantially inthe planes of said limbs and spaced in the direction of electron ow fromsaid limbs forming a first gap between said plates and limbs and spacedfrom said anode forming a second gap between said plates and anode, anda metallic disc sealed into the wall of the device and forming part of ahollow resonator, said disc being positioned between said rst and secondgaps and having an aperture therein to allow of the passage of theelectron stream therethrough.

2. An electron discharge device according to claim 1 wherein the ends ofsaid plates near the anode are brought into close proximity to eachother and are provided with parallel portions which pass through theaperture in the said metallic disc.

3. An electron discharge device according to claim 1 further comprisingmeans for making separable direct electrical contact between said platesand disc, said means being supported on one of said last mentionedelements and adapted to engage the other.

4. An electron discharge device according to claim l further comprisingspring members se'- cured to metallic supporting bars for said platesand adapted to press against said metallic disc for making theelectrical connection therewith.

5. An electron discharge device according to claim 1 further comprisingstraight parallel wires which pass through the envelope of the deviceand arc connected with the cathode and control grid, respectively, toform a low loss path for the input of the device.

6. An electron discharge device according to claim 1 further comprisingan accelerating electrode and a decoupling condenser connected betweensaid accelerating electrode and cathode, said decoupling condenser beingincorporated in the base of said U-shaped member and connected directlyto said accelerating electrode and cathode.

7. An electron discharge device according to claim 1 comprising aconnection between said cathode and said U-shaped member.

8. An electron discharge device according to claim 1 further comprisingan accelerating elec-l trode and the base of said U-shaped membercomprising a double Wall, a decoupling condenser compri-sing a metallicsheet sandwiched between two mica sheets contained within said doublewall, said sheet having two tabs, one connected by a short lead to saidaccelerating electro-de and the other connected to a lead passingthrough the envelope of the device.

JOHN FOSTER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

